Your fitness tracker may claim to measure your sleep, but how accurate is it? To find out, sleep specialist Dr. Christopher Winter tested several popular trackers in a one-night sleep study in his lab.

Of the consumer models, only the Basis accurately tracked sleep and waking time, and detected two out of three REM cycles. Dr. Winter writes, "I am floored that this device accurately staged sleep based solely upon wrist inputs." (It doesn't even require the user to put it into sleep mode.)

Results from the other devices were less impressive, not matching up to actual awakenings or sleep stages. Of course, it's only a one night study done by one man, but the results are quite interesting. Check out the full article below for a graph of the results.